The acid-stable protease inhibitor of human bronchial mucus will be isolated and characterized and its relationship to the inter a1-trypsin inhibitor and other inhibitors of serum will be determined. The site synthesis and Interaction with proteinases will be studied. The typsin inhibiting activity, the concentration of the acid-stable inhibitor and that of a1-antitrypsin in sputum and bronchial mucus will be determined in patients with chronic obstructive pulmonary disease and controls. Proteinase-inhibitor coylesus will be analyzed as to the composition and remaining enzyme activity.